Combustion of propane in air releases a large quantity of heat. Which of the following statements correctly describes the sign of ΔH for the combustion of propane at constant pressure?
a) ΔH is positive because heat released increases the system’s enthalpy.
b) ΔH is negative because heat is transferred from the system to the surroundings.
c) ΔH is positive because the expanding gases perform PΔV work on the surroundings.
d) ΔH is negative only if the reaction is done at constant volume; at constant pressure it becomes positive.